Pros
The real great benefit at IBM is the flexibility to work from anywhere and depending on the position, anytime. Also, the possibility to work with other cultures and languages is really a good advantage if you have the opportunity of working in a global team.
Cons
The compensation plans in IBM are really low comparing to similar on the market. The monthly salary is very low and benefits are far below for a company on that size. The yearly bonus is to make laugh, normally 50% of a salary maximum. The normal benefits, like healthy plans, meals, etc, are only ok, and not as well as anyone should expect for a company on that size. Chances of being promoted are rarely and motivated by the people you know, not the work you do. Your career grows very slowly through the years. Managers usually have more than 200 employees under them, and of course, this is impossible to work like this, so you are on your own. You need to manage yourself and hope that anybody notice you, so you have any chances for promotions and recognition. In the last year or two, the benefits are getting worse, as they cut some of them, and freeze some others.